1. Field of the Invention
The invention relates to the field of microelectromechanical systems (MEMS), and in particular to a CMOS integrated microsensor and a precision measurement circuit for use in such a microsensor.
2. Description of the Prior Art
Very large scale microelectronic products have experienced rapid growth because of the great diversity of system functions which can be provided within a single package. Applications for these devices range from low noise radio circuits through audio, video and high power automotive control systems. However, regardless of the application, all such MEMS rely on the same basic technology components. In particular, the extension of the intrinsically flexible very large scale integrated (VLSI) manufacturing techniques, which when extended to microsensors and microactuators, offers a wide range of new product opportunities. However, in contrast to conventional VLSI systems, microsensor systems must accept a much wider range of input phenomena than conventional electronics. For example, analog and digital VLSI systems, process well-defined electrical input signals. Microsensor systems receive analog and digital electrical inputs, but in addition thereto, must measure temperature, pressure, strain, acceleration, rotation, infrared radiation, chemical properties of liquids and gasses, and a variety of other physical inputs. It is in fact a challenges to develop sensors which respond selectively to only one input. In addition, diverse microsensor manufacturing is complicated by the need for integrating many different structures at a low cost point.
Conventional surface micromachining methods provide combined micromechanical elements and integrated electronics. However, the mechanical structures are inherently microscopic in mass, polycrystalline and typically thin film structures. Thus, for many applications which require large mass, single crystal structures, or materials incompatible with surface micromachining, such as refractory metal oxide piezoelectric or pyroelectric materials, surface micromachining as a process is limited in its scope. In addition, conventional structures and points service micromachining capacitive position sensor are limited by the presence of large parasitic capacitance to the supporting substrate.
Conventional bulk micromachining methods offer precise, single crystal structures which are ideal for many sensing applications and may be compatible with high temperature materials. However, to avoid the attenuating effects of parasitic capacitance, conventionally bulk machine structures have required glass supporting substrates. Typical bulk micromachine devices are not compatible with integrated electronics.
Therefore, what is needed is a process in which microsensors may be manufactured that provides great sensor diversity on a common platform. The process should be able to accommodate new designs and provide a method for eliminating critical electronic measurement limitations which have heretofore seriously constrained conventional surface and bulk micromachined sensor structures.